Low voltage DC-DC converters are useful for power management in battery powered portable electronic devices such as smartphones, tablets, wearable products, etc. DC-DC converters convert a direct current (DC) input voltage into a different DC output voltage. If the DC-DC converter raises the input voltage, then it is known as a boost converter, whereas if it lowers the input voltage, then it is known as a buck converter. If it is capable of operating in either buck mode or boost mode, it is known as a buck-boost converter.
Because the battery voltage of a portable electronic device may vary over a relatively large range, multi-mode buck-boost DC-DC converters have become popular. The most popular multi-mode converter topology is known as the Four Switch Buck Boost Converter (FSBBC) that uses two power switches connected to each terminal of an inductor, one switch on the high side and one switch on the low side of each inductor terminal. During both buck and boost modes of operation, one high-side switch (HSS) remains continuously conductive. For example when operating in the boost mode, the HSS on the input side of the inductor is continuously conductive. Alternatively when operating in the buck mode, the HSS on the output side is continuously conductive. Since the amount of load current is significant and can be, for example, on the order or several amperes, the losses caused by the on resistance (RON) of the HSS that is continuously conductive reduces the efficiency of the converter and shortens battery life.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.